Pseudomonas aeruginosa is among the most dangerous Gram-negative opportunistic pathogens. In the compromised lung, P. aeruginosa is a common cause of ventilator-associated pneumonia, exacerbations in patients with chronic obstructive pulmonary disease, and chronic, lethal infections in individuals with the genetic disease cystic fibrosis. Both chronic and acute P. aeruginosa lung infections are difficult to treat and are associated with high rates of mortality, thus new strategies are needed to combat this bacterium. One important P. aeruginosa virulence factor is a secreted phospholipase C, PlcH, which degrades choline- containing phospholipids, such as phosphatidylcholine (PC), that are highly abundant in the lung. PlcH is cytotoxic, immunomodulatory and causes decreased lung function, and we have discovered a drug, already approved for use in humans, that inhibits PlcH activity, and prevents the effects of PlcH in an acute mouse pneumonia model. Our findings also indicate that P. aeruginosa PlcH-mediated degradation of host phopholipids provides the bacteria with precursors necessary to derive glycine betaine (GB). Through microarray studies, we have found that GB, in addition to being a nutrient and an osmoprotectant, also serves as a novel inducer of Anr, a central transcriptional regulator, in oxic environments where Anr is normally inactive. Our data show a novel role for Anr in biofilm formation and host cell colonization, and that GB stimulation of host colonization is Anr-dependent. Thus, our central hypothesis states that PlcH not only causes host damage, but also releases products that promote P. aeruginosa colonization of the host. Thus, inhibition of PlcH may decrease P. aeruginosa virulence directly and by decreasing antibiotic-resistant biofilms. In this proposal, we aim to test the hypothesis that GB directly increases Anr activity in oxic environments and determine the mechanism by which this occurs (Aim 1) and test the hypothesis that Anr promotes P. aeruginosa biofilm formation and host colonization by increasing the production of CupA fimbriae (Aim 2). In Aim 2, we will also determine if Anr regulation of cupA gene expression is important for P. aeruginosa colonization of the mouse lung, and if there is evidence for GB synthesis, Anr activity, and cupA expression in acute and chronic P. aeruginosa infections in humans. Based on our preliminary data, we predict that the inhibition of PlcH by an existing drug will decrease P. aeruginosa GB levels, biofilm formation and antibiotic resistance, and we will test this hypothesis in Aim 3. Completion of these studies will unravel a new mechanism by which host-derived molecules impact virulence-related gene expression in P. aeruginosa, and may provide insight into the regulation of Anr homologs in other bacterial pathogens. We will pursue the novel and exciting possibility that the use of an exisitng drug that inhibits PlcH activity will both attenuate acute effects of PlcH on the lung and reduce airway colonization by P. aeruginosa rendering it more susceptible to existing antimicrobial therapies. PUBLIC HEALTH RELEVANCE: Pseudomonas aeruginosa is one of the most common causes of hospital-acquired infections and a lethal pathogen of lungs of compromised patients and individuals with CF. Our studies indicate that an enzyme, PlcH, secreted by P. aeruginosa provides the bacterium with a host-derived molecule that serves a novel regulatory role in promoting host colonization. We have discovered a compound, already approved for use in humans, that inhibits PlcH activity in a mouse model, and we will determine if this therapy reduces P. aeruginosa levels in vivo and its resistance to existing antibiotic therapies.